The airways of many breeds of horses, particularly Thoroughbreds, are evaluated via an endoscope and graded before sale. The intent is to identify horses whose airways might have problems that could limit the horses' performance at maximal exercise, so buyers can consider this in their purchasing decisions. At the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla., a study investigating the exam results and later racing performance of 2,954 Thoroughbred yearlings was presented. Scott Pierce, DVM, of Rood & Riddle Equine Hospital in Lexington, Ky., presented the study in an effort to answer the question of just how significant airway grades are.

The exam takes only one to two minutes, and it evaluates arytenoid cartilage function (these cartilages should be able to abduct, or move completely out of the airway to allow maximum airflow) on a scale of 1-4. Epiglottises are also evaluated; a short or otherwise abnormal epiglottis can contribute to dorsal displacement of the soft palate, which can also obstruct airflow. Following are the grading scales Pierce used to evaluate all study horses between 1998 and 2001, and the results.

Arytenoid function (AF)

  • Grade 1: Synchronous movement, symmetrical cartilages; maximal abduction easily achieved. 19% of horses (571) were in this category.
  • Grade 2a: Mildly asynchronous, mildly asymmetrical, maximal abduction easily achieved (70%, 2,068 horses).
  • Grade 2b: Asynchronous, asymmetrical, maximum abduction with difficulty (9%, 260 horses).
  • Grade 3: Asynchronous, asymmetrical, limited arytenoid movement. Full abduction is usually not achieved and especially is not maintained (2%, 55 horses).
  • Grade 4: No arytenoid movement, no abduction. No horses were Grade 4, but Pierce noted that most of these horses would not be offered for sale, as they are usually withdrawn.

Epiglottis structure (ES)

  • Grade 0: Normal epiglottis with good thickness, length, and definition with normally serrated edges. 81% of horses had normal epiglottises.
  • Grade 1: Slightly flaccid, with adequate length and texture, but slightly thinner than normal and without serrated edges (14% of horses).
  • Grade 2: Mildly flaccid, with adequate length, thinner than normal, curled edges and no dorsal vasculature (4% of horses).
  • Grade 3: More severe, moderately flaccid, very thin, and bent easily (1% of horses).
  • Grade 4: Severely flaccid, extremely thin, markedly short, and bent easily (0 horses).

Race records for the 2-, 3-, and 4-year-old years were collected and analyzed in context of the throat exam findings. Pierce reported no difference in the number of starts, earnings per start, or total earnings of horses with Grade 1 vs. Grade 2a arytenoid function at 2, 3, or 4 years of age. Grade 2b horses had significantly lower total earnings per year at 2 and 4 years of age than Grades 1 or 2a, and they had almost significantly lower earnings at Grade 3, but a few big winners in this group kept the numbers at this age from being significant. Grade 3 horses had fewer starts and lower earnings than Grades 1, 2a, and 2b.

Forty-three percent of horses with Grade 3 arytenoid function went unraced, compared to 15% of Grade 2b, 16% of Grade 2s, and 13% of Grade 1.

Horses with epiglottis structure grades of 0-2 all performed about the same, while those with Grades 3 and 4 had significantly decreased earnings at ages 2 and 4.

"So what do I tell clients?" Pierce asked. "I tell them Grades 1 and 2a arytenoids function are no problem. For Grade 2b, there's something there. They don't perform as good as the 1s and 2as; however, if you think the horse is really special, I would buy him anyway. I can't condemn all of these horses. Grade 3s are bad.

"For epiglottis structure, Grades 0-2 are no problem, but I can't recommend horses with higher grades or a really flaccid or short epiglottis," he concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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